My daughter just took an at home uti strip test and it came back positive for leukocytes but negative for nitrates. does this mean she has an infectio?

No: It just means it detected the breakdown products of leucocytes in the sample.You don't mention the age, which is relevant, but most home testing is done wrong.If a woman/girl does a squat pee to collect a sample it is both pee and a vaginal washout.That sample is relatively worthless. Leukocytes can also appear in the urine in any febrile child without infection.